Ganymede: Facts About Jupiter's Largest Moon Ganymede: Facts About Jupiter's Largest Moon By Kim Zimmermann | June 15, 2016 10:53am ET MORE NASA's Voyager 2 spacecraft snapped this color image of Jupiter's moon Ganymede, the largest satellite in the solar system, on July 7, 1979 from a distance of 745,000 miles (1.2 million kilometers). Credit: NASA Jupiter's moon Ganymede is the largest satellite in the solar system. Larger than Mercury and Pluto, and only slightly smaller than Mars, it would easily be classified as a planet if were orbiting the sun rather than Jupiter. The moon likely has a salty ocean underneath its icy surface, making it a potential location for life. The European Space Agency plans a mission to Jupiter's icy moons that in 2030, is planned to arrive and put special emphasis on observing Ganymede. Facts about Ganymede Age: Ganymede is about 4.5 billion years old, about the same age as Jupiter .

Distance from Jupiter: Ganymede is the seventh moon and third Galilean satellite outward from Jupiter, orbiting at about 665,000 miles (1.070 million kilometers). It takes Ganymede about seven Earth-days to orbit Jupiter. [ Photos of Ganymede, Jupiter's Largest Moon ] Size: Ganymede's mean radius is 1,635 miles (2,631.2 km). Although Ganymede is larger than Mercury it only has half its mass, classifying it as low density. Temperature: Daytime temperatures on the surface average minus 171 degrees Fahrenheit to minus 297 F, and night temperatures drop to -193C. In 1996, astronomers using the Hubble Space Telescope found evidence of a thin oxygen atmosphere. However, it is too thin to support life as we know it; it is unlikely that any living organisms inhabit Ganymede. Magnetosphere: Ganymede is the only satellite in the solar system to have a magnetosphere. Typically found in planets, including Earth and Jupiter, a magnetosphere is a comet-shaped region in which charged particles are trapped or deflected.

Ganymede's magnetosphere is entirely embedded within the magnetosphere of Jupiter. This montage compares New Horizons' best views of Ganymede, Jupiter's largest moon, gathered with the spacecraft's Long Range Reconnaissance Imager (LORRI) and its infrared spectrometer, the Linear Etalon Imaging Spectral Array (LEISA). Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute Discovery and exploration of Ganymede Ganymede was discovered by Galileo Galilei on Jan. 7, 1610. The discovery, along with three other Jovian moons , was the first time a moon was discovered orbiting a planet other than Earth. Galileo's discovery eventually led to the understanding that planets orbit the sun, instead of our solar system revolving around Earth. Galileo called this moon Jupiter III. When the numerical naming system was abandoned in the mid-1800s, the moon was named after Ganymede, a Trojan prince in Greek mythology. Zeus, a counterpart of Jupiter in Roman mythology, carried Ganymede, who had taken the form of an eagle, to Olympus, where he became a cupbearer to the Olympian gods and one of Zeus' lovers.

Several spacecraft have flown by Jupiter and its moons. Pioneer 10 arrived first, in 1973, followed by Pioneer 11 in 1974. Voyager 1 and Voyager 2 returned striking photos during their flybys. The Galileo spacecraft passed as low as 162 miles (261 km) over the surfaces of the Galilean moons and produced detailed images. The European Space Agency plans a mission called JUICE (JUpiter ICy moons Explorer) that would launch from Earth in 2022 for arrival at Jupiter in 2030. While the mission will look at three moons (Ganymede, Callisto and Europa), Ganymede will be the focus because it shows how icy worlds evolve and could be habitable in general, ESA said on its website. Scientists will try to figure out more about its ocean and icy crust, map its surface in detail, learn about the interior, probe the atmosphere and study the magnetic field.

Ganymede sound and signal illustration Characteristics of Ganymede Ganymede has a core of metallic iron, which is followed by a layer of rock that is topped off by a crust of mostly ice that is very thick. There are also a number of bumps on Ganymede's surface, which may be rock formations. In February 2014, NASA and the United States Geological Survey unveiled the first detailed map of Ganymede in images and a video animation created using observations from NASA's Voyager 1 and Voyager 2 spacecraft, as well as the dedicated Jupiter-orbiting Galileo spacecraft. Ganymede's surface is made up of primarily two types of terrain: about 40 percent is dark with numerous craters, and 60 percent is lighter in color with grooves that form intricate patterns to give the satellite its distinctive appearance. The grooves, which were likely formed as a result of tectonic activity or water being released from beneath the surface, are as high as 2,000 feet and stretch for thousands of miles. A global image mosaic of Jupiter's moon, Ganymede created with images from the Voyager and Galileo missions.

Credit: Wes Patterson It is believed that Ganymede has a saltwater ocean below its surface. In 2015, a study by the Hubble Space Telescope looked at Ganymede's auroras and how they change between Ganymede's and Jupiter's magnetic fields. The “rocking” seen by the auroras gives evidence that the probable ocean underneath is salty , more salty than oceans of Earth, scientists said at the time. Some scientists are skeptical that Ganymede could host life, however. Due to its internal structure, it is believed that the pressure at the base of the ocean is so high that any water down there would turn to ice . This would make it difficult for any hot-water vents to bring nutrients into the ocean, which is one scenario under which scientists believe extraterrestrial life would occur. Additional reporting by contributor Elizabeth Howell. Additional resource Ganymede (Moon) Facts Ganymede Eris Ganymede Moon Facts Ganymede is Jupiter’s largest moon and also the largest moon in the solar system. Ganymede was discovered in 1610 by astronomer Galileo Galilei and is named for the mythical Greek son of a King who was carried to the sky by Zeus posing as an eagle.

Ganymede Moon Profile 1.48 x 10^23 kg (2.0 Moons) Orbits: Ganymede size compared to the Moon and Earth Jupiter’s Galilean moons size comparison (Io, Europa, Ganymede and Callisto) Facts about Ganymede Ganymede is the largest moon in the solar system, and is larger than the planet Mercury. If it were not orbiting as Jupiter’s second-largest moon, it could be considered a dwarf planet. Ganymede is the only moon in the solar system known to have a substantial magnetosphere. That implies there is something inside helping to generate a strong magnetic field. Like Europa, Ganymede is thought to have a subsurface ocean, overlying a liquid iron and nickel core. That core is what helps generate the magnetic field. The surface of Ganymede is icy and covered with two main types of landscape: young, lighter regions and darker, older and cratered terrain. The dark areas appear to contain clays and organic materials. Ganymede was likely formed in place around the infant Jupiter in the early solar system. Several smaller worlds likely accreted together to make this moon.

Ganymede has a thin atmosphere that appears to contain oxygen. This was confirmed by Hubble Space Telescope observations. The oxygen is likely freed as water ice on the surface is broken apart into hydrogen and oxygen by solar radiation. The first mission to explore Ganymede up close was Pioneer 10, followed by the Voyager missions, Galileo, and New Horizons. Several missions to explore Ganymede in more detail have been suggested, but most have been cancelled or are still on the drawing boards. Sources: Ganymede Moon Facts Ganymede is the 7th moon in distance from Jupiter. It is the largest moon in the solar system. It has a diameter of 3,270 miles (5,262 km) which is larger than the planet Mercury. Ganymede orbits Jupiter at a distance of 665,116 miles (1,070,400 km) and takes 7 days 3 hours to make one orbit of the planet. It is the only moon in the solar system known to have its own magnetic field. The moon has polar caps, possibly caused by ice interacting with plasma being funnelled down its magnetic field and creating a layer of frost.

Ganymede has a low density meaning that even though it is bigger than Mercury it only has half its mass. Ganymede's low mass is as a result of water ice making around half its composition. Jupiter's gravity pushes and pulls at the moon causing underground friction, possibly producing one or maybe even two layers of salty liquid oceans under its surface. The moon was discovered in January 1610 by the Italian astronomer Galileo Galilei. An image of impact craters on Ganymede's surface revealing the moon's icy crust. Ganymede's Surface Ganymede has two types of ancient surface, both of which have been unchanged for billions of years. Forty percent is made up of darker areas which are highly cratered. The remaining sixty percent consists of lighter areas marked by grooved terrains. Some of these grooves are over 700 meters (2,000 feet) in height and run for thousands of miles across its surface. Ganymede's Atmosphere Ganymede has an extremely thin atmosphere consisiting of dispersed oxygen molecules.

Ganymede's Temperature Daytime temperatures on the surface average around -113C to -183C (-171F to -297F). At night temperatures plunge even further to around -193C (-315F). Life on Ganymede Where water exists on Earth we find life and the same could be said of Ganymede if the moon does indeed possess underground oceans. Proving this would be a very difficult task though as the layers of liquid would be very deep below the surface and covered with thick ice. Origin of Name Ganymede is named after a handsome mortal prince from Greek mythology who was abducted by Zeus to become cup-bearer to the gods. Missions to Ganymede JUICE (JUpiter ICy moon Explorer) Launch: 2022 Arrival: 2030 Agency: ESA (European Space Agency) Summary: The JUICE probe will study the Jovian system, focusing on the icy moons of Europa, Callisto and Ganymede, investigating any potential habitable environments. The probe will enter into orbit around Ganymede in the latter part of the mission, studying its icy surface and subsurface ocean.

It will also observe how Ganymede's magnetic field interracts with Jupiter's magnetosphere. New Horizons Arrival: January 2007 Agency: NASA Summary: As well as sending back images New Horizons made topography and composition maps of Ganymede. Galileo Arrival: December 1995 Agency: NASA Summary: Galileo made several flybys of Ganymede sending back a whole host of new data. As well as discovering a magnetic field, an ocean underneath its surface was also detected. Galileo also sent back some stunning close up images of the moon. Voyager 1 and 2 Arrival: April-August 1979 Agency: NASA Summary: Voyager 1 and 2 made successful flybys of Ganymede taking far more detailed images than the previous Pioneer missions. The grooved terrain could be seen and it was also revealed that Ganymede was in fact larger than first thought, replacing Saturn's moon Titan as the largest satellite in the solar system.

Pioneer 10 and 11 Launch: March 1972 - April 1973 Arrival: December 1973 - December 1974 Agency: NASA Summary: Pioneer 10 and 11 made successful flybys of Ganymede but only sent back limited data and blurry images such as the one on the left. Share this page The moon Ganymede - Comparison, history, geography, structure, exploration The moon Ganymede Ganymede. © based on NASA images Ganymede is the largest moon around the planet Jupiter. Ganymede is also the biggest moon in the solar system. Ganymede is roughly three thousand miles across, making it bigger than the planet Mercury. If Ganymede was orbiting the Sun, it would be considered a planet. Ganymede is large enough to be pulled into a sphere by its gravity. Ganymede compared with other objects of Solar System. © based on NASA images Ganymede orbits Jupiter every 7.16 days. Its orbit has an average distance of 665,000 miles or a million kilometers from Jupiter. Its orbit is close to Jupiter’s equator.

Ganymede is tidally locked, presenting the same face to Jupiter as it rotates. This means that Ganymede’s “day” is the same as its orbit, just over 7 days long. Jupiter rising over Ganymede with Io and Europa. © NASA Ganymede has a very circular orbit around Jupiter. It also has minimal orbital inclination. Ganymede is one of the three moons of Jupiter that is in a stable Laplace resonance. For each orbit of Ganymede, Europa orbits twice while Io orbits four times. Because we know that there is an ocean under Europa’s surface and its approximate volume, scientists have used the overall density of Europa to assume that there is a solid core under the ice that is half as wide as the moon’s total diameter. Since Ganymede is about 5,300 miles across, the solid core would be about 2,650 miles across. History of Ganymede Ganymede has areas on its surface as old as the solar system, up to 4.5 billion years old. The gradual erosion of its surface and odd patterns of grooves and cracks are what led scientists to discover its underground ocean.

Ganymede was one of the four moons of Jupiter discovered by Galileo in 1610. Fellow astronomer Simon Marius named it Ganymede for a Greek child who served as a cup-bearer to Zeus or Jupiter, king of the Gods. The moons of Jupiter were initially assigned numbers. The name Ganymede was unofficial from the start but became official in the early 1800s. Geography of Ganymede We know that Ganymede has a liquid water ocean under its icy exterior. Ganymede does not have a volcanic core heated by the decay of radioactive elements like Earth and Venus. Instead, Ganymede’s core is heated by the gravitational tug of war between Jupiter and the other moons around Jupiter. Ganymede is the only moon to our knowledge to have a magnetic field. This may be a sign of a molten magnetic core, albeit much smaller than Earth’s. The surface of Ganymede is relatively smooth. It has craters from meteor impacts. However, anything large that breaches the frozen surface causes water to fill it. Ganymede has an infinitesimal atmosphere.

Saturn’s moon Titan has a full atmosphere composed of hydrocarbons, including ethane clouds and methane rain. Ganymede’s atmosphere contains traces of oxygen, probably the result of ice on the surface broken down into molecular hydrogen and oxygen. Hydrogen has a lower escape velocity, leaving the traces of oxygen behind. There are also traces of ozone, caused by particles crashed into Ganymede‘s atmosphere propelled by Jupiter’s magnetic field. Internal structure of Io, Europa, Ganymede and Callisto. © based on NASA images Ganymede has areas that are up to 4.5 billion years old. And there are much younger areas marked by grooves and look like filled in cracks. This terrain may be the result of slow moving ice flows on the Ganymede surface. Or they may result from tidal forces causing seismic shifts similar to tectonic plates on Earth. Where a break or crack occurs, the frozen slush rises up and fills in the crack creating a relatively smooth groove that runs for hundreds of miles. The primary landmark on Ganymede is a large crater called Anat. However, there are many smaller craters sprinkled across Ganymede.

The older portions of Ganymede’s surface, those not filled in by ice water below, have more craters than the newer portion of the planet surface. Craters that have been nearly completely worn away or filled in reveal that Ganymede’s surface is still changing with time. Ganymede has no large mountains caused by impact craters like Earth’s moon, since there was no hot, molten rock to be blasted into the atmosphere upon impact. Any mountains that did occur were worn down to low ridges. Life on Ganymede? Surface of Ganymede. © NASA We do not know if Ganymede holds life under its thick icy exterior. However, it has many of the prerequisites we think life needs. Liquid water exists. The planet has an ocean that contains more water than Earth’s oceans, though at far greater pressures than even the bottom of the Mariana Trench in the Pacific Ocean. It has energy in the form of a molten interior. Ganymede is theoretically a more stable home for life, since it will be warmed by tidal heating by Jupiter long after the Earth’s core cools while the thick layers of ice protect any ocean life instead from asteroid strikes like the one that wiped out the dinosaurs.

Ganymede has a rocky core and rock mixed in with the ice, providing elements similar to those available to undersea life. This means that Ganymede has the potential of evolving sea life similar to those that live at the bottom of Earth’s ocean, living off of undersea thermal vents. Life on Ganymede would evolve without needing sunlight, since none penetrates the thick ice of Ganymede. In this way, Ganymede is similar to Europa as a potential home for life in our solar system. Exploration of Ganymede Jupiter's Moon Ganymede - Universe Today Universe Today by Matt Williams In 1610, Galileo Galilei looked up at the night sky through a telescope of his own design . Spotting Jupiter, he noted the presence of several “luminous objects” surrounding it, which he initially took for stars. In time, he would notice that these “stars” were orbiting the planet, and realized that they were in fact Jupiter’s moons – which would come to be named Io , Europa , Ganymede and Callisto . Of these, Ganymede is the largest, and boasts many fascinating characteristics.

In addition to being the largest moon in the Solar System, it is also larger than even the planet Mercury. It is the only satellite in the Solar System known to possess a magnetosphere, has a thin oxygen atmosphere, and (much like its fellow-moons, Europa and Callisto) is believed to have an interior ocean. Discovery and Naming: Though Chinese astronomical records claim that astronomer Gan De may have spotted a moon of Jupiter (probably Ganymede) with the naked eye as early as 365 BCE, Galileo Galilei is credited with making the first recorded observation of Ganymede on January 7th, 1610 using his telescope. Together with Io, Europa and Callisto, he named them the “Medicean Stars” at the time – after his patron, the Grand Duke of Tuscany, Cosimo de’ Medici. Simon Marius, a German astronomer and contemporary of Galileo’s who claimed to have independently discovered Ganymede, suggested alternative names at the behest of Johannes Kepler. However, the names of Io, Europa, Ganymede and Callisto – which were all taken from classical mythology – would not come to formally be adopted until the 20th century.

Illustration of Jupiter and the Galilean satellites. Credit: NASA Prior to this, the Galilean Moons were named Jupiter I through IV based on their proximity to the planet (with Ganymede designated as Jupiter III). Following the discovery of the moons of Saturn, a naming system based on that of Kepler and Marius was used for Jupiter’s moons. In Greek mythology, Ganymede was the son of King Tros (aka. Ilion), the namesake of the city of Troy (Ilium). Size, Mass and Orbit: With a mean radius of 2634.1 ± 0.3 kilometers (the equivalent of 0.413 Earths), Ganymede is the largest moon in the Solar System and is even larger than the planet Mercury. However, with a mass of 1.4819 x 10²³ kg (the equivalent of 0.025 Earths), it is only half as massive. This is due to Ganymede’s composition, which consists of water ice and silicate rock (see below).

Ganymede’s orbit has a minor eccentricity of 0.0013, with an average distance (semi-major axis) of 1,070,400 km – varying from 1,069,200 km at periapsis to at 1,071,600 km apoapsis. Ganymede takes seven days and three hours to completes a single revolution. Like most known moons, Ganymede is tidally locked, with one side always facing toward the planet. Its orbit is inclined to the Jovian equator, with the eccentricity and inclination changing quasi-periodically due to solar and planetary gravitational perturbations on a timescale of centuries. These orbital variations cause the axial tilt to vary between 0 and 0.33°. Ganymede has a 4:1 orbital resonance with Io and a 2:1 resonance with Europa. Ganymede is the largest satellite in our solar system, larger than Mercury and Pluto, and three-quarters the size of Mars. Credit: NASA/JPL Essentially, this means that Io orbits Jupiter four times (and Europa twice) for every orbit made by Ganymede.

The superior conjunction between Io and Europa occurs when Io is at periapsis and Europa is at apoapsis, and the superior conjunction between Europa and Ganymede occurs when Europa is at periapsis. Such a complicated resonance (a 4:2:1 resonance) is called the Laplace Resonance . Composition and Surface Features: With an average density of 1.936 g/cm3, Ganymede is most likely composed of equal parts rocky material and water ice. It is estimated that water ice constitutes 46–50% of the moon’s mass (slightly lower than that of Callisto) with the possibility of some additional volatile ices such as ammonia being present. Ganymede’s surface has an albedo of about 43%, which suggests that water ice makes up a mass fraction of 50-90% the surface. Near-infrared and ultra-violet surveys have also revealed the presence of carbon dioxide, sulfur dioxide, and possibly cyanogen, hydrogen sulfate and various organic compounds. More recent data has shown evidence of salts such as magnesium sulfate and possibly sodium sulfate, which may have originated from the subterranean ocean (see below).

Ganymede’s interior appears to be fully differentiated, consisting of a solid inner core made of iron, a liquid iron and iron-sulfide outer core, a silicate mantle, and a a spherical shell of mostly ice surrounding the rock shell and the core. The core is believed to measure 500 km in radius, and has a temperature of about 1500 – 1700 K and pressure of up to 10 GPa. Artist’s cut-away representation of the internal structure of Ganymede, with layers shown to scale. Credit: Wikipedia Commons/kelvinsong The most compelling evidence for the existence of a liquid, iron-nickel-rich core is Ganymede’s intrinsic magnetic field. The convection in the liquid iron, which has high electrical conductivity, is the most reasonable model of magnetic field generation.The density of the core is believed to be 5.5 – 6 g/cm³, while the silicate mantle has an estimated density of 3.4 – 3.6 g/cm³. This mantle is composed of silicate materials, most likely chondrites and iron.

The outer ice shell is the largest layer of all, measuring an estimated 800 km (497 miles) thick. The precise thicknesses of this and other layers in the interior of Ganymede depends on the assumed composition of silicates and amount of sulfur in the core. Scientists also believe that Ganymede has a thick ocean nestled between two layers of ice – a tetragonal layer between it and the core and a hexagonal layer above it. The presence of this ocean has been confirmed by readings taken by orbiters and through studies of how Ganymede’s aurora behaves. In short, the moon’s auroras are affected by Ganymede’s magnetic field, which in turn is affected by the presence of a large, subsurface salt-water ocean. Ganymede’s surface is a mix of two types of terrain. There’s the very old, highly cratered, and dark regions, and the somewhat younger, lighter regions marked with an extensive array of grooves and ridges. In a way that is similar to Europa, Ganymede’s surface is asymmetric, with the leading hemisphere being brighter than the trailing one.

The dark terrain, which comprises about one-third of the surface, is so-colored because the surface ice in these regions contains clays and organic materials. It has been theorized that these have been left behind by impactors, which accords with the fact that impact craters are far more extensive in the areas of dark terrain. Meanwhile, the grooved terrain is believed to be tectonic in nature; which could be due in part to cryovolcanism , but is thought to be mostly the result of tidal heating events. The tidal flexing could have heated the interior and strained the lithosphere, leading to the development of cracks, graben and faults that erased the old, dark terrain on 70% of the surface. Though craters are more common in the darker areas, they are seen all over the surface. Ganymede may have experienced a period of heavy cratering 3.5 to 4 billion years ago similar to that of the Moon. If true, the vast majority of impacts happened in that epoch, whereas the cratering rate has been much smaller since.

Craters on Ganymede are also flatter than those on the Moon and Mercury, which is probably due to the relatively weak nature of Ganymede’s icy crust. Ganymede also has polar caps, likely composed of water frost, which were first seen by the Voyager spacecraft. Since the discovery, several theories have been proposed for their formation, ranging from the thermal migration of water vapor to higher latitudes to plasma bombardment turning the ice brighter. Data obtained by the Galileo spacecraft – which noted a very close correspondence between the polar cap boundary and the boundaries of the moon’s magnetic field – suggests that the latter theory is correct. Atmosphere: Similar to Europa, Ganymede has a tenuous oxygen atmosphere. Also similar to Europa is how the atmosphere formed, which involves water ice on the surface being split into hydrogen and oxygen through interaction with UV radiation, the hydrogen being lost to space and the oxygen being retained. The surface pressure of this atmosphere is thought to lie within the range of 0.2–1.2 micro Pascals. Montage showing New Horizons’ views of Ganymede taken by it’s infrared spectrometer and LORRI and LEISA instruments.

Credit: NASA/Johns Hopkins University APL/SwRI The presence of this atmosphere also causes an airglow effect, a faint emission of light caused by the interaction of atomic oxygen and energetic particles. This effect is not uniformly distributed (as with Europa), but instead causes bright spots to appear above the polar regions – which could be “polar auroras” – due to the planet’s magnetic field. Additional evidence of the oxygen atmosphere comes from the detection of various gases trapped in the ice on Ganymede. This evidence consisted of the spectroscopic detection of ozone (O³), as well as absorption features that indicated the presence of oxygen gas (O²). Another constituent of the atmosphere is hydrogen, which (despite most being lost to space) still exists at a surface in very minor concentrations. The existence of this neutral atmosphere implies that an ionosphere should exist since oxygen molecules are ionized by the impacts of the energetic electrons coming from the magnetosphere and by solar electromagnetic UV radiation. However, the existence of an ionosphere remains controversial, due to conflicting data gathered by different missions. Magnetosphere: Ganymede is unique among moons in the Solar Systems in that it alone has a magnetosphere.

The value of the moon’s permanent magnetic moment is estimated to be 1.3 x 10¹³ T·m³, which is three times larger than the magnetic moment of Mercury. The magnetic dipole is tilted with respect to the rotational axis of Ganymede by 176°, which means that it is directed against the Jovian magnetic moment. The magnetic field of Jupiter and co-rotation enforcing currents. Credit: Wikipedia Commons/Ruslik0 The dipole magnetic field created by this permanent moment has a strength of 719 ± 2 Teslas (nT) at Ganymede’s equator, and roughly twice that at the poles (1440 nT). This magnetic moment also carves a part of space around Ganymede, creating a tiny magnetosphere embedded inside that of Jupiter with a diameter of about 10,525 – 13,156 km. The Ganymedian magnetosphere has a region of closed field lines located below 30° latitude, where charged particles (electrons and ions) are trapped, creating a kind of radiation belt.

The main ion species in the magnetosphere is single ionized oxygen, which fits well with Ganymede’s tenuous oxygen atmosphere. The interaction between the Ganymedian magnetosphere and Jovian plasma is in many respects similar to that of the solar wind and Earth’s magnetosphere. The plasma co-rotating with Jupiter impinges on the trailing side of the Ganymedian magnetosphere much like the solar wind impinges on the Earth’s magnetosphere. In addition to the intrinsic magnetic moment, Ganymede has an induced dipole magnetic field who’s existence is connected with the variation of the Jovian magnetic field near Ganymede. The induced magnetic field of Ganymede is similar to those of Callisto and Europa, indicating that this moon also has a subsurface water ocean with a high electrical conductivity. Artist’s concept of aurorae on Ganymede. Credit: NASA/ESA However, the existence of Ganymede’s magnetosphere remains a bit of a mystery. On the one hand, its existence is believed to be the result of Ganymede’s a dynamo effect caused by conducting material moving in the core, similar to Earth.

However, other bodies that have differentiated metallic cores don’t have magnetospheres, and the relatively small size of Ganymede’s core suggests that it should have cooled sufficiently that fluid motions are no longer possible. One explanation for this incongruity is that the same orbital resonances that may have disrupted the surface also allow the magnetic field to persist. With tidal heating increasing during such resonances, the mantle may have insulated the core, preventing it from cooling. Another explanation is a remnant magnetization of silicate rocks in the mantle, which is possible if the satellite had a more significant dynamo-generated field in the past. Habitability: There is some speculation on the potential habitability of Ganymede’s ocean. An analysis published in 2014 , taking into account the realistic thermodynamics for water and effects of salt, suggests that Ganymede might have a stack of several ocean layers separated by different phases of ice, with the lowest liquid layer adjacent to the rocky mantle below. This is important, since the layer closest to the rocky interior would be subject to heating due to tidal flexing in the mantle. This heat could be transferred into the water via hydrothermal vents , which could provide the necessary heat and energy to sustain life.

Combined with oxygenated water, life forms could exist at the core-mantle boundary in the form of extremophiles, in a way that is similar to what is found in Earth’s oceans (and presumed to exist in Europa’s interior ocean). Exploration: Several probes flying by or orbiting Jupiter have explored Ganymede more closely, including four flybys in the 1970s, and multiple passes in the 1990s to 2000s. The first approaches were conducted by the Pioneer 10 and 11 probes, which approached the moon in 1973 and 1974, respectively. These missions returned more specific information on its physical characteristics and resolved features to 400 km (250 mi) on its surface. The next missions came in 1979, when the Voyager 1 and 2 probes passed the moon, refining estimates of its size and revealing its grooved terrain for the first time. In 1995, the Galileo spacecraft orbited Jupiter and went on to make six close flybys between 1996 and 2000.

The probe’s findings included the discovery of Ganymede’s magnetic field, the moon’s interior ocean, and a large number of spectral images that showed non-ice compounds on the surface. Artist impression of New Horizons conducting its flyby of Jupiter. Image credit: NASA/JPL/JHUAPL The most recent mission to Ganymede was made by the New Horizons probe in 2007. While en route to Pluto, the probe obtained topographic and composition mapping data of Europa and Ganymede during its flyby of Jupiter. Their are no missions to Ganymede currently in operation, but several missions have been proposed for the coming decades. One such proposal is the joint NASA/ESA Europa Jupiter System Mission (EJSM), which would explore Jupiter’s moons (including Ganymede) and has a proposed launch date of 2020. The mission would consist of NASA’s Jupiter Europa Orbiter, the ESA’s Jupiter Ganymede Orbiter, and possibly a JAXA Jupiter Magnetospheric Orbiter.

The ESA’s contribution was renamed the Jupiter Icy Moon Explorer (JUICE) in 2012, and obtained a launch slot aboard the ESA’s Cosmic Vision science program (scheduled for launch in 2022 or 2024). This may include a partner mission from the Russian Space Research Institute – known as the Ganymede Lander (GL) – and would involve JUICE examining Ganymede from orbit and conducting multiple flybys or Europa and Callisto. A Ganymede orbiter based on the Juno probe was also proposed in 2010 for the Planetary Science Decadal Survey. As part of the committee report presented at the Survey – titled “ Vision and Voyagers for Planetary Science in the Decade 2013-2022 ” – a concept study for a possible Ganymede Orbiter was proposed, which included recommendations on instrumentation. Artist’s concept of the Jupiter Icy Moons Orbiter (JIMO), a cancelled program that envisioned sending a spacecraft to inspect Callisto, Ganymede and Europa.

Credit: NASA/JPL A canceled proposal for a Ganymede orbiter was the Jupiter Icy Moons Orbiter (JIMO), which would have performed a flyby of Europa, Ganymede and Callisto. Designed to use nuclear fission for power and an ion engine for propulsion, JIMO would have studied Ganymede in greater detail than an previous orbiter. However, the mission was canceled in 2005 because of budget cuts. Colonization: Ganymede is considered a possible candidate for human settlement – and even terraforming – due to the many advantages it presents. For one, as Jupiter’s largest moon, Ganymede has a gravitational force of 1.428 m/s2 (the equivalent of 0.146 g) which is comparable to Earth’s Moon. Sufficient enough to limit the effects of muscle and bone degeneration, this lower gravity also means that the moon has a lower escape velocity – which means it would take considerably less fuel for rockets to take off from the surface. What’s more, the presence of a magnetosphere means that colonists would be better shielded from cosmic radiation than on other bodies.

The prevalence of water ice means that colonists could also produce breathable oxygen, their own drinking water, and would be able to synthesize rocket fuel. Unfortunately, beyond this, Ganymede presents numerous challenges for colonization. For starters, the presence of a magnetosphere does not shield Ganymede from enough cosmic radiation to ensure human safety, due to the fact that it is overshadowed by Jupiter’s powerful magnetic field. This results in the surface receiving some 8 rem of radiation per day – which is 333 times the average of what Earth-bound organisms experience in a year. Artist’s concept for a future settlement on Ganymede. Credit: futuretimeline.net The dominance of Jupiter’s magnetic field also means that Ganymede’s magnetosphere is not strong enough to retain an atmosphere of sufficient density to sustain human beings. It would also be insufficient to retain much heat. Hence, settlements on the surface would need to be heavily insulated, shielded from radiation, and contain a breathable atmosphere. A possible solution to this, similar to what has been proposed for Europa, would be for colonists to build settlements within the icy mantle, or possibly under the surface of the ice entirely.

These embedded (or aquatic habitats) would be shielded from harmful cosmic radiation by the icy mantle. They could also function as conduits between the ocean and the surface, piping water in and processing it into fuel for export. However, such possibilities are still far from realization and in the meantime, exploring Ganymede and deciphering its deeper mysteries remains the priority. And of these, Ganymede has several! Much like the other Galilean moons, Ganymede possesses a wealth of unique and mysterious attributes, many of which still defy comprehension. In addition to being the largest moon in the Solar System, it is the only moon other than Earth (and the gas giants) to have a magnetic field. And of course, there’s the possibility that life could exist beneath its icy crust, possibly in microbial or extreme form. All of these make Ganymede an intriguing prospect for future exploration. We have many interesting articles on Ganymede and Jupiter’s Moons here at Universe Today. Here is a list of the Galilean Moons , as well as Jupiter’s entire system of moons . Here is one about Ganymede’s interior ocean , and how an amateur astronomer made a detailed map of Ganymede .

Here’s a list of all the largest moons in the Solar System, and a listing of the largest moons and smallest planets at Solar Views. Universe Today has whole series of podcasts about the Solar System at Astronomy Cast . Share this: The Galilean Moons of Jupiter The Galilean Moons of Jupiter Summary: Jupiter has more than 60 known moons, but understanding the geology of its four largest will hopefully lead to some groundbreaking discoveries. Sections: The Galilean Moons Each of the Jovian planets has a number of moons, although Jupiter has the most with more than 60 catalogued to date. Jupiter's 4 largest moons exhibit some of the most interesting geology in the solar system. They were discovered by Galileo Galilei and are known as the Galilean moons. Jupiter's largest moon, Ganymede, is larger than Mercury while the other three are larger than Pluto. Outward from Jupiter: Io: Volcanoes and All Jupiter's Moon Io The Voyager spacecraft took the first close-up images of Io more than 300 years after the moon's discovery. The images showed a surface with no signs of craters from past impacts.

What we saw instead was a surface almost entirely covered with large volcanoes. Cameras on Voyager actually captured volcanic eruptions in progress. The frequency of these sulfuric eruptions has filled in almost all of the impact craters and left Io with one of the youngest looking surfaces in the solar system. Io Close-Up (click to enlarge) Close-up photos of eruptions in progress show powerfully hot lava glowing orange and red. Photos taken on the night side of Io show not only the hot volcanic vents, but also a thin sulfur dioxide atmosphere produced by constant outgassing. Io's unusual red and orange colors come primarily from sulfur, which condenses on the surface after being outgassed by the volcanoes. Although there is no direct evidence of tectonic activity on Io, scientists feel confident it exists since the processes that fuel volcanism also fuel tectonics. The volcanic eruptions are so frequent and cover the surface so thoroughly that any clear evidence of tectonic activity is likely to be buried. Europa: What Lies Beneath? Europa Europa's surface and crust are made almost entirely of water ice, and its bizarre, fractured appearance is proof enough that tidal heating has acted there.

The icy surface is nearly devoid of impact craters and may be only a few million years old. Europa's Interior Observations made by the Galileo spacecraft show that Europa has a metallic core and a rocky mantle. Surrounding the rocky interior appears to be an icy layer 100 kilometers thick, the top few kilometers of which seem to be frozen solid. The stretching and squeezing of tidal friction should provide enough heat to melt some of this into liquid water beneath a thin ice shell. If it does, then Europa may have an ocean with more than twice as much liquid water as all of Earth's oceans combined. Analyzing Europa's Cracked Surface Close-up photos of the surface of Europa support the idea of a liquid ocean beneath the surface. These photos, taken by the Galileo spacecraft, show what appears to be icebergs stuck in a layer of ice. Other evidence comes from double-ridged cracks on the surface. Tidal flexing that allows water to well up and build ridges may create these cracks. Ganymede: Largest Moon in the Solar System Two Regions of Ganymede's Surface (click to enlarge) The surface of Ganymede shares many similarities with Europa.

Ganymede's surface is also made of water ice, but unlike Europa's surface, it shows signs of varying age. The darker regions are heavily cratered, suggesting they are billions of years old. The lighter regions show no signs of craters and it is thought that eruptions of water covered the surface before freezing over. These areas are geologically younger than the darker regions. If liquid water occasionally makes its way to the surface to fill in craters, could that suggest a liquid ocean similar to the one that might exist on Europa? Callisto: The Outermost Galilean Moon Callisto Callisto is the stereotypical outer solar system satellite. It is one of the largest and most heavily cratered satellites in the solar system. The surface is very icy and dates back four billion years. Beneath the icy crust is possibly a salty ocean supported by a deeper rocky interior. Callisto's Surface Callisto doesn't have any large mountains, show evidence of volcanic or tectonic activity or have any appreciable level of internal heat. Nonetheless, observations of Callisto's magnetic field may cause scientists to add the large moon to the list of possible worlds with subsurface salty oceans.

Jupiter's Moon Ganymede Ganymede This shows an entire hemisphere of Ganymede. The prominent dark region, called Galileo Regio, is about 3,200 km in diameter. The bright spots are relative recent impact craters. Part of the Galileo Regio may be covered with a bright frost. (Copyright Calvin J. Hamilton) The Interior of Ganymede Voyager images were used to create a global view of Ganymede. The cut-out reveals the interior structure of this icy moon. This structure consists of four layers based on measurements of Ganymede's gravity field and theoretical analyses using Ganymede's known mass, size and density. Ganymede's surface is rich in water ice and Voyager and Galileo images show features which are evidence of geological and tectonic disruption of the surface in the past. As with the Earth , these geological features reflect forces and processes deep within Ganymede's interior.

Based on geochemical and geophysical models, scientists expected Ganymede's interior to either consist of: a) an undifferentiated mixture of rock and ice or b) a differentiated structure with a large lunar sized 'core' of rock and possibly iron overlain by a deep layer of warm soft ice capped by a thin cold rigid ice crust. Galileo's measurement of Ganymede's gravity field during its first and second encounters with the huge moon have basically confirmed the differentiated model and allowed scientists to estimate the size of these layers more accurately. In addition the data strongly suggest that a dense metallic core exists at the center of the rock core. This metallic core suggests a greater degree of heating at sometime in Ganymede's past than had been proposed before and may be the source of Ganymede's magnetic field discovered by Galileo's space physics experiments. (Copyright 1999 by Calvin J. Hamilton) Southern Galileo Regio This image of southern Galileo Regio shows impact craters in various stages of degradation. Almost all of the craters appear flat. The two prominent light colored craters are almost completely erased by the flow in the icy crust. (Copyright Calvin J.

Hamilton) Craters, Light and Dark Bands This image of Ganymede was taken by Voyager 1 , 246,000 kilometers (158,000 miles) from the planet. The center of the picture is at 19° south latitude and 356° longitude, and the height of the frame represents a distance of about 1000 kilometers (600 miles) on the surface. The smallest features seen on this picture are about 2.5 kilometers (1.5 miles) across. The surface displays numerous impact craters many of which have extensive bright ray systems. The craters lacking ray systems are probably older than those showing rays. Bright bands traverse the surface in various directions and these bright bands contain an intricate system of alternating linear bright and dark lines which may represent deformation of the crusted ice layer. These lineations are particularly evident near the top of the picture. A bright band trending in a north-south direction in the lower left-hand portion of the picture is offset along a bright line. This offset is probably due to faulting.

Two light circular areas in the right upper center of the picture may be the scars of ancient impact craters which have had their topographic expansion erased by flowage of the crystal icy material. (Image Copyright Calvin J. Hamilton) Temperature Map of Ganymede This map shows the temperatures for most of the surface of Ganymede made from data taken by the Photopolarimeter/Radiometer (PPR) instrument on June 26, 1996 as Galileo approached the sunlit side of the moon. The color bar shows the range of temperatures of this data, with the dark red being the coldest and white being the warmest. This is similar to the temperature forecast maps that you see on the evening news or in some newspapers. The difference between this map and one of Earth is that PPR measures the temperature of the surface (the ground), instead of air temperature. Ganymede is much colder than Earth, with these daytime temperatures ranging across the surface from 90 to 160 Kelvin (or -297 to -171 degrees Fahrenheit).

Jupiter and its moons receive less than 1/30th the amount of sunlight that the Earth does, and Ganymede has essentially no atmosphere to trap heat. Ganymede's day is just over 7 Earth days long, the same time it takes to orbit Jupiter once. (Courtesy NASA/JPL) Ganymede: Facts about Jupiter's Moon, Ganymede Interactive Solar System Model Ganymede Facts Ganymede is the seventh moon of Jupiter and the third of the Galilean moons. It is the largest moon in the solar system and is larger than the planet Mercury and dwarf planet Pluto . Ganymede is only slightly smaller than Mars and if it were orbiting the Sun rather than Jupiter , it would be classified as a planet itself. Ganymede was discovered by Galileo Galilei on 7 January 1610 along with the three other Jovian moons Europa, Io and Callisto . Together they are referred to as the Galilean moons. The discovery of these four Galilean satellites are what eventually led to the understand that the planets in the solar system were orbiting the Sun and that Earth was not the centre of the solar system.

Size of Ganymede compared to Jupiter Side by side comparison of the size of Jupiter vs it’s moon Ganymede Facts about Ganymede If Ganymede were orbiting the Sun it would be a planet. Ganymede is larger than both Mercury and Pluto, and is 2/3 the size of Mars with a diameter of 5,268 km (3,273 miles) – 8% larger than Mercury. It has the highest mass of all planetary satellites and has more than twice the mass of the Earth’s Moon. The moon is named after a Trojan prince in Greek mythology. Originally called Jupiter III by Galileo, Ganymede was named after a suggestion from German mathematician and astronomer Johannes Kepler. In the Greek story Zeus, a counterpart of Jupiter in Roman mythology, carried the prince Ganymede to Olympus, where he became a cupbearer for the Olympian gods. It takes Ganymede 7.1 Earth days to orbit Jupiter at a speed of 39,165 km/h.

The moon orbits at 39,165 km (24,321 miles) an hour and takes 7.15455296 Earth days to complete its orbit around Jupiter. Like most moons in the solar system, Ganymede is tidally locked to Jupiter and one side is always facing the planet. Interestingly, for every orbit of Ganymede, Europa orbits Jupiter twice and Io orbits four times. Ganymede is the only moon in the solar system known to have its own magnetic field. It is believed that the magnetosphere of Ganymede is likely to have been created through convection within the liquid iron core of the moon. The field is very small though and is barely noticeable because it is buried within Jupiter’s much larger magnetic field. The moon is composed of equal amounts silicate rock and water ice and has several layers. Ganymede is made of rocky material and water ice. It has a metallic iron and iron sulfide core which is surrounded by a rocky mantle and a very thick icy crust. There may be an ocean layer of liquid water beneath the surface of Ganymede.

An study published in 2014 suggests that there might be a stack of several saltwater ocean layers separated by different phases of ice as far as 124 miles below the surface of Ganymede. The lowest liquid layer may be right next to the rocky mantle below and could be sign for sustainable life on Ganymede. 40% of Ganymede’s surface is covered with highly cratered dark regions. These dark regions are believed to be from heavy impact by asteroids or comets and date back to around 4 billion years ago. The lighter regions of the moon’s surface are not quite so old and cover the rest of Ganymede. The cause of the light terrain’s disrupted geology is though to be the result of tectonic activity caused by tidal heating – a build up of friction, orbital and rotational energy that are dissipated as heat in the crust of the moons and planets involved. Ganymede has a thin atmosphere than contains oxygen. The moon has a very thin atmosphere and it does contain small amounts of oxygen but there is not enough to support any form of life. Six spacecraft have visited Ganymede since 1973.

Pioneer 10 and 11 were launched in March 1972 and April 1973 respectively and made successful flybys of Ganymede in December 1973 and December 1974. They sent back limited data with blurry images of the moon. Voyager 1 and 2 returned much more high quality and detailed images in 1979 which showed the grooved terrain and also discovered that Ganymede was larger than first thought – replacing Saturn’s moon Titan as the largest satellite in the solar system. The Galileo spacecraft in 1995 passed as low as 162 miles (261 km) over the surfaces of the Galilean moons, sending back a lot of new data such as the discovery of the magnetic field, the ocean beneath Ganymede’s surface, and the highest resolution close up images of the moon. Finally, New Horizons in 2007 sent back images and made topography and composition maps of Ganymede before continuing on towards Pluto and the Kuiper Belt . Ganymede Profile AmazingSpace - How to use in the classroom Use this resource as: A source of information.

Read the table to find out about this object. A large-number recognition and ordering activity. Have students review several Fast Fact moon tables, including this one. Have students read the tables to find each object's mass. Then ask them to arrange the objects according to their mass, from smallest to largest. Students also can arrange the objects according to their diameter. A math activity. Use Newton's law of gravitation, the distance between Io and Jupiter, and the masses of the two objects to determine the gravitational force between them. (Recommended for grades 10-12) An inquiry tool. Have students write down questions they would like answered about the image and the information in the Fast Facts table. An engagement tool. Involve students in a discussion. Related materials Jupiter's Moon Ganymede Has a Salty Ocean with More Water than Earth Jupiter's Moon Ganymede Has a Salty Ocean with More Water than Earth By Miriam Kramer, Space.com Staff Writer | March 12, 2015 01:50pm ET MORE In this artist’s conceptual illustration, the moon Ganymede orbits giant planet Jupiter. NASA’s Hubble Space Telescope detected auroras on the moon controlled by Ganymede's magnetic fields.

Image released March 12, 2015. Credit: NASA/ESA A salty ocean is lurking beneath the surface of Jupiter's largest moon, Ganymede, scientists using the Hubble Space Telescope have found. The ocean on Ganymede — which is buried under a thick crust of ice — could actually harbor more water than all of Earth's surface water combined, according to NASA officials. Scientists think the ocean is about 60 miles (100 kilometers) thick, 10 times the depth of Earth's oceans, NASA added. The new Hubble Space Telescope finding could also help scientists learn more about the plethora of potentially watery worlds that exist in the solar system and beyond. "The solar system is now looking like a pretty soggy place," Jim Green, NASA's director of planetary science, said during a news teleconference today (March 12). Scientists are particularly interested in learning more about watery worlds because life as we know it depends on water to thrive. [ See amazing photos of Ganymede ] Scientists have also found that Ganymede's surface shows signs of flooding.

Young parts of Ganymede seen in a video map may have been formed by water bubbling up from the interior of the moon through faults or cryo-volcanos at some point in the moon's history, Green said. NASA Hubble Space Telescope images of Ganymede's auroral belts (colored blue in this illustration) lie on top of a Galileo orbiter image of the moon. The amount of rocking of the moon's magnetic field supplied evidence that the moon possesses a subsurface saltwater ocean. Image released March 12, 2015. Credit: NASA/ESA Scientists have long suspected that there was an ocean of liquid water on Ganymede — the largest moon in the solar system, at about 3,273 miles (5,268 kilometers) across — has an ocean of liquid water beneath its surface. The Galileo probe measured Ganymede's magnetic field in 2002, providing some data supporting the theory that the moon has an ocean. The newly announced evidence from the Hubble telescope is the most convincing data supporting the subsurface ocean theory yet, according to NASA.

Scientists used Hubble to monitor Ganymede's auroras, ribbons of light at the poles created by the moon's magnetic field. The moon's auroras are also affected by Jupiter's magnetic field because of the moon's proximity to the huge planet. When Jupiter's magnetic field changes, so does Ganymede's. Researchers were able to watch the two auroras "rock" back and forth with Hubble. Ganymede's aurora didn't rock as much as expected, so by monitoring that motion, the researchers concluded that a subsurface ocean was likely responsible for dampening the change in Ganymede's aurora created by Jupiter. "I was always brainstorming how we could use a telescope in other ways," Joachim Saur, geophysicist and team leader of the new finding, said in a statement. "Is there a way you could use a telescope to look inside a planetary body? Then I thought, the aurorae! Because aurorae are controlled by the magnetic field, if you observe the aurorae in an appropriate way, you learn something about the magnetic field.

If you know the magnetic field, then you know something about the moon's interior." Hunting for auroras on other worlds could potentially help identify water-rich alien planets in the future, Heidi Hammel, executive vice president of the Association of Universities for Research in Astronomy, said during the teleconference. Scientists might be able to search for rocking auroras on exoplanets that could potentially harbor water using the lessons learned from the Hubble observations of Ganymede. This cross-sectional illustration shows the interior of Jupiter's largest moon Ganymede, based on theoretical models, in-situ observations by NASA's Galileo orbiter, and Hubble Space Telescope observations of the moon’s magnetosphere. Image released March 12, 2015. Credit: NASA, ESA, and A. Feild (STScI) Astronomers might be able to detect oceans on planets near magnetically active stars using similar methods to those used by Saur and his research team, Hammel added. "By monitoring auroral activity on exoplanets, we may be able to infer the presence of water on or within an exoplanet," Hammel said.

"Now, it's not going to be easy — it's not as easy as Ganymede and Jupiter, and that wasn't easy. It may require a much larger telescope than Hubble, it may require some future space telescope, but nevertheless, it's a tool now that we didn't have prior to this work that Joachim and his team have done." Jupiter's moons are popular targets for future space missions. The European Space Agency is planning to send a probe called JUICE — short for JUpiter ICy moons Explorer — to Jupiter and its moons in 2022. JUICE is expected to check out Europa, Callisto and Ganymede during its mission. NASA also has its eye on the Jupiter system. Officials are hoping to send a probe to Europa by the mid-2020s. NASA will also celebrate the Hubble telescope's 25th anniversary this year. "This discovery marks a significant milestone, highlighting what only Hubble can accomplish," John Grunsfeld, assistant administrator of NASA's Science Mission, said in the same statement . "In its 25 years in orbit, Hubble has made many scientific discoveries in our own solar system.

A deep ocean under the icy crust of Ganymede opens up further exciting possibilities for life beyond Earth."

Question: Ganymede is the largest moon in the solar system, around which planet does it orbit?
Answer: Jupiter